Computer-aided design (CAD) is a fairly recent advancement in the drafting and design process. While CAD shortened the production time for drafting, it still necessitated complex and laborious procedures to perform parametric design. The techniques were awkward to learn, difficult to use and lacking in power. The only comprehensive approach made use of programming language to write a special purpose program which could both design and draw. Establishing such a design was time consuming and awkward. Other approaches lacked power and could not truly perform parametric design. As a result, an informed operator was required to guide their process during a design's execution. Executing such a design was awkward and prone to error.
Furthermore, CAD did not have the capability of combining data representing different parts or modules of an overall design. This is a significant drawback as all assemblies, and even many parts, can most expeditiously be designed by treating them as integrated aggregations of modular features, parts, and/or sub-assemblies.
Representative of the heretofore proposed CAD systems is the one disclosed in U.S. Pat. No. 4,549,275 issued Oct. 22, 1985, to Sukonic for GRAPHICS DATA HANDLING SYSTEMS FOR CAD WORKSTATION
A competing system which utilizes computer aid in design creation is disclosed in U.S. Pat. No. 4,451,895 issued June 9, 1983, to sleikowski for INTER-ACTIVE COMPUTER AIDED DESIGN. This system is of even less interest than CAD systems such as those disclosed in the above-identified Sukonic patent, in part because it is not capable of generating parametric designs.
Another computer-aided design technique that has heretofore been employed involves the parametric enhancement of drawing editing, a technique which makes use of drawing processors. Certain drawing processwors such as the AUTOCAD.RTM. and the Hewlett-Packard, Euchlid, and Medusa processors, have extremely powerful editing capabilities which include elements of parametric design. However, these all share the limitation that the user is dealing with one detail, or at most, one drawing, at a time.
There are two approaches to the above mentioned-parametric enhancement of drawing editing.
The first is the built-in language approach. To create a unique image, the user must write program code which describes the geometry of the drawing in terms of its coordinates such as the two end points of a line. The built-in language approach has the additional disadvantages that the user can create only one drawing as a result of running a design.
This is undesirable because most designs are depicted in a series of related drawings. For example describing a particular part might entail depicting it in several views: It might be depicted individually (in order to provide details describing the part itself); then again in an assembly drawing (in order to show its physical relationship to surrounding parts); and finally, in a concept drawing (in order to show its function).
The second approach makes use of drawing rectification. Rectification is an editing capability. To rectify a drawing is to make it correct according to its dimensions; i.e. the drawing is modified and brought into conformity with its dimensions. Using this enhancement to drawing editing as a basis for parametric design, the user employs equations in the dimensions of the drawing in place of fixed values. The equations, which may involve trigonometric formulas, relate the geometry of different parts of the drawing to one another.
The user can automatically edit the drawing by entering the drawing processor and providing values corresponding to the independent variables in these equations. The user can even use a computer program from outside the drawing processor to calculate these values.
The drawing rectification approach contains the following problems:
1. The design process is not controlled by the computer. This means the user must be educated as to his or her role in producing a particular design. Since the user has to control the process, the chance of a procedural error being introduced is greatly increased.
2. The user, rather than the program, must design which drawing to rectify in order to depict the design. Choosing the appropriate parameterized picture, the single most important decision in the process, is left up to the user. An informed user is required as he or she must be aware of the current inventory of parameterized drawings. The process of choosing the appropriate design is awkward and relatively slow.
3. This approach limits the depiction of the design to a single drawing. Most designs cannot be depicted with a single drawing.
4. Since the user is editing an image on the drawing processor, there is a great probability that he will inadvertently change an aspect of the original drawing, introducing an error into the image being edited.